Not a mechanic, but most motors need to turn between 5000 - 5500 rmp @ WOT. If you run it WOT how many rpm are you turning? Sounds like a lower pitch would help some. Montauk is probably the best on the site to give info.
I think you may have another problem burning that much gas. Is tank built in? When did you fill up? How much do you normally use?
I know, more questions than answers.
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